This invention relates to shell and tube heat exchangers. More specifically, this invention relates to a two-pass shell and tube heat exchanger with a U-tube bundle.
Shell and tube heat exchangers have long been known as useful tools for heating fluids and using thermal energy. Such shell and tube heat exchangers have been developed to a significant degree of sophistication. These heat exchangers comprise a shell surrounding a tube bundle usually attached to a tube sheet. Fluid flowing through the shell is subjected to indirect heat exchange with another fluid flowing through the tubes.
Because of their low shell side, pressure loss characteristics, heat exchangers having two shell side-fluid passes are increasingly being used in gas services and as feedwater heaters. Two shell-pass arrangements, containing a longitudinal plate along the shell axis, are also used to produce pure counterflow and to avoid temperature crosses, which may occur in conventional, single shell-pass arrangements. The most common tube bundle configuration for a two shell-pass geometry is a U-tube bundle. In a two shell-pass arrangement, an axial plate is installed inside the shell of a shell and tube heat exchanger to form a longitudinal baffle. This longitudinal baffle produces two distinct shell side flow passages, i.e., an inlet and an exit passage. In such a configuration, fluid enters the shell through a single nozzle at the tube sheet end of the exchangers, flows axially through the shell side inlet passage, experiences a 180.degree. flow reversal at the end of the longitudinal baffle, and flows axially back to the exit nozzle through the exit shell side flow passage. In a U-tube bundle, this flow reversal occurs in the U-bend region of the tube bundle, where U-bend supports are normally required for tube vibration protection. In such an arrangement, these supports of the U-bend region can create excessive flow obstructions and pressure losses. If, however, U-bend supports are not utilized in the U-bend region, fluid flow through the U-bend region can create flow-induced vibration in the tube bundle.
An important object of the present invention is to provide a two pass shell and tube heat exchanger having a U-tube bundle in which the U-bend region may be properly supported, while eliminating excessive flow obstructions and associated pressure losses and with reduced tendency for flow-induced vibration in the U-bend region.
Another object of this invention is to provide a two pass shell and tube heat exchanger having a U-tube bundle in which the tendency for flow-induced vibration in the U-bend region will be reduced.
Another object of this invention is to provide a shell unit for use in a two pass shell and tube heat exchanger having a U-tube bundle which will allow fluid flow through the shell unit without excessive flow obstructions and associated pressure losses.
Other and further objects, aims, purposes, features, advantages, embodiments, and the like will be apparent to those skilled in the art from the present specification, taken with the associated drawings, and the appended claims.